An Orthogonal Frequency Division Multiplexing (OFDM) method, such as Long Term Evolution (LTE), standardized by 3rd Generation Partnership Project (3GPP) attracts attention as a communication method for the next generation. In a communication method such as LTE, a receiver needs to report reference signal received power (RSRP) to a higher-level layer, as stipulated in NPL1. On the basis of such information as RSRP that a receiver estimates, it is judged whether a handover process is performed between base stations or not. In order to perform the handover process with an appropriate base station, it is needed to improve the accuracy of power estimation by the receiver.
In a conventional communication method of Code Division Multiple Access (CDMA), a measurement of RSRP is performed by way of in-phase addition of pilot signals after Rake combining, for example, as described in NPL2. Then, in order to improve the estimation accuracy, proposed are, for example, a method of estimating RSRP with a high degree of accuracy by using a signal before Rake combining, as described in PTL1; as well as another method that applies a value with high accuracy while concurrently using in-addition and root-mean-square of received signals, as described in PTL2.
Unfortunately, in a communication method of OFDM for concurrently transmitting information by using a plurality of sub-carriers (sub-carrier waves), channel estimation values turns if an offset exists on the timing of FFT (Fast Fourier Transformation). Therefore, if in-phase addition is performed with those channel estimation values as they are, sometimes RSRP may be estimated to be smaller than it should actually be. FIG. 5 shows such an example. NPL3 discloses an introduction of a method in which in-phase addition is performed after conjugate multiplication between neighboring channel estimation values, for solving such a challenge.
On the other hand, LTE needs to estimate RSRP with accuracy stipulated in NPL4. Meanwhile, it is difficult for the method disclosed in NPL3 to estimate RSRP with accuracy that meets those stipulated specifications.